It is known to mount a sleeve-that contains a magnetic material such as ferrite onto a neck of A CRT for correcting static convergence, color purity and geometry errors in the CRT. A manufacturer of the ferrite magnetic material either extrudes a heated magnetic material through a rectangular slit die or rolls the material into sheets. In both cases, long coils of belt-like sheath material are provided to the CRT manufacturer. The sheets are cut into strips. The edges of a given strip are spliced, using a securing tape, to form a spliced cylindrical shape that is mounted on a funnel of the CRT to form a sleeve or sheath.
Beam landing correction is accomplished by the creation of various combinations of magnetic poles in the ferrite material that produce static or permanent magnetic fields. The magnetic fields vary the beam landing location in the CRT. The magnetic pipe sheath is referred to as a sheath beam bender (SBB). The SBB can correct for mount seal rotation in the CRT.
A magnetizer head is used at the factory for magnetizing the SBB. The SBB is used to create two, four and six pole vertical and horizontal corrections to the electron beams at different planes perpendicular to the electron beam path. For example, two plane correction is called Blue Bow and is a result of a pair of four pole vertical corrections.
A SBB, embodying an inventive feature, is formed from a seamless magnetic sheath, for example, by extrusion by using an extrusion die. Alternatively, a high pressure injection mold may be used for producing an injection molded seamless SBB. Advantageously, the seamless nature of the sheath eliminates tape bumps and rough splice joints associated with prior art arrangements. Thereby, advantageously, closer contact between the magnetizer head that is used at the factory and the SBB is facilitated. Advantageously, the use of the seamless pipe sheath eliminates SBB gap. It eliminates SBB edge-to-edge misalignment, thus improving Yoke Adjustment Machine (YAM) yield. It eliminates an overlap splice hump that restricts magnetizer head closure causing magnetizer error rejects. Cost reduction is obtained by the elimination of the need for using a securing tape. Advantageously, it is readily adaptable to robotic application. Cost reduction also results from the ability to recycle pipe sheaths on product that is set up more than once. Advantageously, the need to position the gap of the sheath, occurring with some prior art arrangements, is no longer of concern because the sheath material is seamless.
A deflection yoke mounted on the CRT may include an auxiliary Beam Scan Velocity Modulation (BSVM) coil. On a very larger size (VLS) CRT, where the deflection yoke is mechanically attached to the funnel of the CRT, a prior art SBB is typically taped directly onto the funnel using two pieces of Mylar tape. Afterwards, a wire-wound BSVM coil, placed on a plastic carrier, is mechanically attached over the top of the SBB.
In carrying out a further inventive feature, by using, for example, the injection mold technique, an integrated SBB/BSVM combination device having seamless SBB is obtained. The integrated SBB/BSVM combination device having seamless SBB that is formed by injection mold technique can utilize solid conductor wire wound BSVM molded into sheath material. Such arrangement may be, advantageously, less costly. Also, this permits placing the BSVM coil closer to the electron gun. Thereby, advantageously, the BSVM sensitivity is improved by eliminating the thickness of a prior art plastic carrier.